Fiber-reinforced plastic (FRP) attracts attention in various industrial fields as light-weighted and high-strength material. In recent years, to produce a relatively large fiber-reinforced plastic molding at a low cost, there has been employed a vacuum assist resin transfer molding (VaRTM) for molding fiber-reinforced plastic under a depressurized atmosphere by means of vacuum suction. The vacuum assist resin transfer molding is a method for obtaining a fiber-reinforced plastic molding including the steps of covering a dry fiber fabric arranged in a molding die with a bag film, vacuuming the air inside the bag, infusing a liquid resin into the bag film, impregnating the dry fiber fabric with resin, and curing the resin (for example, refer to PTD1: Japanese Patent Laying-Open No. 60-83826).
However, since a dry fiber fabric has no tackiness (viscosity), the dry fiber fabric itself cannot be fixed at a position against gravity in the step of shaping into a three-dimensional shape (the step of arranging a dry fiber fabric on a molding die and the step of laminating a dry fiber fabric on a dry fiber fabric). Further, when a dry fiber fabric and a molding die, or a dry fiber fabric and a dry fiber fabric are not in sufficient contact with each other, fibers in some cases exhibited wrinkles under the depressurized condition.
As a simplified method for solving such a problem, a method is conceivable using a tape to fix a portion being subject to trimming and not eventually used in a finished product. However, there is a problem that a portion which can be fixed using a tape is limited, and that the operation is cumbersome and results in low productivity.
Therefore, there have been proposed a method for fixing a dry fiber fabric through use of a solution with a binder containing an amorphous thermoplastic resin (tackifier: spray) (for example, refer to PTD2: Japanese Patent Laying-Open No. 2004-269705) and a method for shortening the step of laminating dry fiber fabrics by adhering a plurality of dry fiber fabrics to each other in advance by means of an adhesive resin composed of a mixture of a thermoplastic resin (toughness) and thermosetting resin (for example, refer to PTD3: Japanese Patent Laying-Open No. 2004-114586).
The method disclosed in PTD2 can be used in the step of arranging a dry fiber fabric on a molding die and in the step of laminating a dry fiber fabric on a dry fiber fabric, allowing the operation time to be shortened. However, when the method is used in the step of arranging a dry fiber fabric on a molding die, a non-cured thermoplastic component is exposed at the surface of a demolded fiber-reinforced plastic molding. Therefore, there has been a problem that the surface which was in contact with the molding die may become sticky and that a thermoplastic component may exhibit white dots to cause poor appearance.
Further, the method disclosed in PTD3 can be used in the step of laminating a dry fiber fabric on a dry fiber fabric, allowing the operation time to be shortened. However, the method cannot be used in the step of arranging a dry fiber fabric on a molding die. Further, when a plurality of dry fiber fabrics are combined in advance, and a large number of layers are present, shaping at a bent portion becomes difficult. Particularly, the tension applied to the fiber will differ between the inside and outside, resulting in occurrence of wrinkles due to loosening of fibers.
Furthermore, with the method disclosed in PTD 3 in which a bonding resin containing a thermoplastic resin as a main component is used, heating for welding is required. Moreover, a thermoplastic resin which melts at a relatively low temperature is disadvantageous in heat resistance. On the other hand, when a high melting temperature thermoplastic thermoplastic resin is used, lamination of dry fiber fabrics is possible, but it is difficult to fix a dry fiber fabric to a molding die. The high melting temperature thermoplastic resin has insufficient tackiness particularly to a molding die having been subjected to mold release processing. Moreover, with the method disclosed in PTD 3, it is not easy to cut a dry fiber fabric into an intended shape.